Open-label Study of ELA026 in Participants With Secondary Hemophagocytic Lymphohistiocytosis (sHLH)

Key Inclusion Criteria for Part 1:

1. ≥12 years at the time of HLH diagnosis (Cohort 1).

2. ≥6 years at the time of HLH diagnosis (Cohort 2-3).

3. Treatment naïve or relapsed/refractory (Cohorts 1 and 2).

4. Treatment naïve or early refractory (Cohort 3).

5. Participant with sHLH confirmed criteria based on fulfilling 5 out of 8 HLH-2004 diagnostic criteria.

Key Inclusion Criteria for Part 2:

1. ≥18 years old, with treatment-naïve mHLH, diagnosed by HLH-2004 criteria, triggered by any type of malignancy (Cohort A).

2. ≥18 years old ≥12 to 17 years old with treatment-naïve sHLH, diagnosed by HLH-2004 criteria, not triggered by any type of malignancy (Cohort B).

3. ≥18 years old, with treatment-naïve mHLH, diagnosed by biomarker criteria but not meeting HLH-2004 criteria, triggered by any type of malignancy (Cohort B).

4. 13 to 17 years old with treatment-naïve sHLH, diagnosed by HLH-2004 criteria, due to any trigger (Cohort B).

5. 6 to 12 year old, with refractory sHLH, diagnosed by HLH-2004 criteria due to any trigger (refractory defined as ≤ 2 weeks of HLH-directed therapy with suboptimal response as determined by the investigator - safety lead-in cohort).

6. 6 to 12 year old treatment-naïve sHLH diagnosed by HLH-2004 criteria due to any trigger.

Key Exclusion Criteria for Part 1:

1. Known or previous treatment for primary HLH

2. Any other significant concurrent, uncontrolled medical condition that in the opinion of the Investigator contraindicates participation in this study

3. Unknown trigger for sHLH

4. Active, relapsed/refractory malignancy for which no suitable therapies are available to treat the malignancy triggering the HLH

5. Allogeneic hemopoietic stem cell transplant (HSCT) within 100 days of the first dose of ELA026.

6. Ongoing administration of any therapies used to treat HLH (excluding dexamethasone)

7. Live or attenuated vaccine received within 6 weeks or bacille Calmette-Guerin (BCG) vaccine within 12 weeks prior to Screening

Key Exclusion Criteria for Part 2:

1. Refractory sHLH (except for the safety lead-in cohort for 6-12 year old in Cohort B).

2. Known or suspected primary or hereditary HLH.

3. Severe organ dysfunction.

4. Any other significant concurrent, uncontrolled medical condition that contraindicates participation in this study or prohibits completion of study procedures.

5. End-stage malignancy for which no suitable therapies are available to treat the malignancy triggering the HLH.

6. Allogeneic hemopoietic stem cell transplant within 100 days prior to the first dose of ELA026 or within 30 days of study enrollment.